#include <iostream>
#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <unistd.h>
#include <sys/wait.h>
#include <sys/types.h>

#define COMMAND_SIZE 1024
#define FORMAT "%s@%s:%s$ "

// 下面是shell定义的全局数据
#define MAXARGC 128
char* g_argv[MAXARGC];
int g_argc = 0;

// 环境变量表
#define MAX_ENVS 100
char* g_env[MAX_ENVS];
int g_envs = 0;

// for test
char cwd[1024];
char cwdenv[1024];


int lastcode = 0;

const char* GetUserName()
{
	const char* name = getenv("USER");
	return name == NULL ? "None" : name;
}

const char* GetHostName()
{
	const char* hostname = getenv("HOSTNAME");
	return hostname == NULL ? "None" : hostname;
}

const char* GetPwd()
{
	//const char* pwd = getenv("PWD");
	const char* pwd = getcwd(cwd, sizeof(cwd));
	if(pwd != NULL)
	{
		snprintf(cwdenv, sizeof(cwdenv), "PWD=%s", cwd);
		putenv(cwdenv);
		return "None";
	}
	return pwd == NULL ? "None" : pwd;
}

const char *GetHome()
{
	const char* home = getenv("HOME");
	return home == NULL ? "" : home;
}

void InitEnv()
{
	extern char** environ;
	memset(g_env, 0, sizeof(g_env));
	g_envs = 0;

	// 本来要从配置文件来
	// 1.获取环境变量
	for(int i = 0; environ[i]; i++)
	{
		// 1.1 申请空间
		g_env[i] = (char*)malloc(strlen(environ[i]) + 1);
		strcpy(g_env[i], environ[i]);
		g_envs++;
	}
	g_env[g_envs] = NULL;

	// 2. 导成环境变量
	for(int i = 0; g_env[i]; i++)
	{
		putenv(g_env[i]);
	}
}

bool Cd()
{

	if(g_argc == 1)
	{
		std::string home = GetHome();
		if(home.empty()) return true;
		chdir(home.c_str());
	}
	else
	{
		std::string where = g_argv[1];
		if(where == "-")
		{
		}
		else if(where == "~")
		{
		}
		else
		{
			chdir(where.c_str());
		}
	}
	return true;	
}

void Echo()
{

	if(g_argc == 2)
	{
		std::string opt = g_argv[1];
		if(opt == "$?")
		{
			std::cout << lastcode << std::endl;
			lastcode = 0;
			
		}
		else if(opt[0] == '$')
		{
			std::string env_name = opt.substr(1);
			const char* env_value = getenv(env_name.c_str());
			if(env_value)
			{
				std::cout << env_value << std::endl;
			}
		}
		else
		{
			std::cout << opt << std::endl;
		}
	}
}

std::string DirName(const char* pwd)
{
#define SLASH "/"
	std::string dir = pwd;
	if(dir == SLASH) return SLASH;
	auto pos = dir.rfind(SLASH);
	if(pos == std::string::npos) return "BUG?";
	return dir.substr(pos + 1);
}	

void MakeCommandLine(char cmd_prompt[], int size)
{
	snprintf(cmd_prompt, size, FORMAT, GetUserName(), GetHostName(), DirName(GetPwd()).c_str());
}

void PrintCommandPrompt()
{
	char prompt[COMMAND_SIZE];
	MakeCommandLine(prompt, sizeof(prompt));
	printf("%s", prompt);
	fflush(stdout);
}

bool GetCommandLine(char* out, int size)
{
	// ls -a -l => "ls -a -l\n" 字符串
	char* c = fgets(out, size, stdin);
	if(c == NULL) return false;
	out[strlen(out) - 1] = 0; // 清理\n
	if(strlen(out) == 0) return false;
	return true;
}

bool CommandParse(char* commandline)
{
#define SEP " "
	g_argc = 0;
	g_argv[g_argc++] = strtok(commandline, SEP);		
	while(g_argv[g_argc++] = strtok(nullptr, SEP));
	g_argc--;
	return g_argc > 0 ? true : false;
}

void PrintArgv()
{
	for(int i = 0; g_argv[i]; i++)
	{
		printf("argv[%d]-> %s\n", i, g_argv[i]);
	}
}

int Execute()
{
	pid_t id = fork();
	if(id == 0)
	{
		execvp(g_argv[0], g_argv);
		exit(1);
	}
	int status = 0;
	
	pid_t rid = waitpid(id, &status, 0);
	if(rid > 0)
	{
		lastcode = WEXITSTATUS(status);
	}
	(void)rid; 
	return 0;
}

bool CheckAndExecuteBuiltin()
{
	std::string cmd = g_argv[0];
	if(cmd == "cd")
	{
		Cd();
		return true;
	}
	else if(cmd == "echo")
	{
		Echo();
		return true;
	}

	return false;
}

int main(int argc, char* argv[])
{
	// shell 启动的时候，从系统中获取环境变量
	// 我们的环境变量信息应该从父 shel 统一来
	InitEnv();
	
	while(true)
	{
		// 1. 输出命令行提示符
		//printf("%s@%s:%s$", GetUserName(), GetHostName(), GetPwd());
		PrintCommandPrompt();

		// 2. 获取用户输入的命令
		char commandline[COMMAND_SIZE];
		if(!GetCommandLine(commandline, sizeof(commandline)))
		{
			continue;
		}
		//printf("echo: %s\n", commandline);

		// 3. 命令行分析
		if(!CommandParse(commandline))
		{
			continue;
		}
		//PrintArgv();

		// 4. 检测并处理內键命令
		if(CheckAndExecuteBuiltin())
		{
			continue;
		}

		// 5. 执行命令
		Execute();
	}

	return 0;
}
